1. Field of the Invention
The present invention relates to plastics packaging equipment. More particularly, the present invention relates to bottle coating equipment.
2. Description of the Related Art
One of the greatest challenges in the plastics packaging business has been the reduction of gas transfer through polymeric materials to either stop gases from ingressing into the packaged product, or to stop gases from egressing from the packaged product. There have been many approaches attempted including new resin formulations and multi-layers of polymeric materials, but each has had problems finding widespread acceptance due to either the cost, non-recyclability or the performance.
Traditionally, polyester terephthalate (PET) is the polymer of choice when gas barrier is needed in plastic packaging. In the three-dimensional (or rigid packaging area), PET is used in almost all applications where shelf-life and clarity are required although poly propylene (PP) is also frequently used.
Rigid packaging, sometimes called three-dimensional packaging, includes bottles, cans, cups and typically excludes the so-called flexible packaging. Examples of flexible packaging include pouches, and bags.
Although widely used in rigid packaging, PET and PP are limited in their ability to provide gas barrier to both gas coming into the product (gas ingress) and escaping (gas egress). In the case of beer, a highly oxygen sensitive beverage, even the oxygen that is adsorbed in the wall of the PET/PP bottle can significantly alter the taste and shelf-life of the beer. For carbonated soft drinks (CSD), on the other hand, the barrier must stop carbon dioxide from escaping out of the beverage and there are little to no concerns about the ingress of gases.
One conventional approach to providing barriers in PET/PP bottles is surface coating technologies where a thin layer is applied to the interior and/or exterior surface of the PET/PP bottle. With this approach, thin film coatings are deposited by chemical vapor deposition utilizing plasma enhanced chemical vapor deposition (PECVD), where the coating is derived from gases that are decomposed within the bottle by a plasma.
To insure that the thin film coating provides an adequate barrier, it is important that the thin film coating cover the entire interior and/or exterior surface of the bottle. However, the thin film coating is transparent and thin, typically on the order of 20 to 500 nm. Thus, it is not possible to determine whether the entire interior and/or exterior surface of the bottle has been coated with the thin film coating from a visual observation of the bottle with the naked eye.